Fluid propellant mill with fluid jets in the sifting zone



J. WOELLHAF July 3, 1955 FLUID PROPELLANT MILL WITH FLUID JETS IN THE. SIFTING ZONE Filed Feb. 18, 1955 INVENTQR. JOS EF WOE LLHAF States FLUID PRUPELLANT MILL WITH FLUID JETS IN THE SIFTING ZONE Josef Woellhaf, Ludwigshafen (Rhine), Germany, assignor to Badische Anilin- 8; Soda-Fabrik Aktiengesellnchaft, Ludwigshafen (Rhine), Germany This invention relates to an improved grinding process.

For the production of an extremely fine grinding it is known to use circular grinding chambers in which the material to be ground is kept in circulating movement by jets of propellants. By the jets of propellant introduced with the aid of nozzles, a strong rotational movement is caused in the grinding apparatus by which the coarser particles are continually thrown out to the Wall of the grinding chamber while only the finest particles can leave the mill.

We have now found that in a grinding process of the kind described above, a considerably higher degree of fineness and a greater uniformity of the grinding can be obtained by allowing additional jets of propellant to enter a sifting zone situated between the grinding zone and the outlet, the said additional jets imparting to the circulating material in the sifting zone an increased rotational speed whereby the coarser particles are returned to the grinding zone.

The additional jets of propellant entering the sifting zone are directed in one or more planes perpendicular to the axis of the grinding apparatus which are different from the plane or planes in which the jets of propellant entering the grinding zone lie, or are directed obliquely to such plane or planes.

The manner in which the process according to this invention may be carried out will now be described with reference to the accompanying drawings.

Fig. l-A and Fig. 1-B show a vertical and horizontal section, respectively, of a grinding apparatus according to this invention. Material to be comminuted is introduced through an opening 2 into a circular grinding chamber l. A propellant gas, as for example air, nitrogen, superheated steam or the like, is blown into the grinding chamber through nozzles 3. it is advantageous for the jets of propellant to form an acute angle with the tangents to the outer wall of the grinding chamber. The material to be ground is set in a strongly rotating motion by the propellant gas, and as a consequence the individual particles are comminuted by friction against each other and by collision with each other. The sufiiciently comminuted particles are carried by the propellant gas in a spiral path into the middle of the grinding chamber which acts as a sifting chamber. into this sifting zone there is blown further propellant through nozzles 4 and this imparts an increased rotational speed to the particles circulating in the sitting zone. The consequence is that the coarser particles are thrown back again into the grind ing zone while only the finest particles are expelled through openings 5. The sifting zone '7 annexed to the grinding zone 6 is widened in the embodiment shown in Figure l-A in order to prevent the force of entrainment being increased by the amounts of propellant additionally introduced into this zone. The widening is effected in such a manner that projecting edges 8 are formed at which the larger particles of the material to be ground, which tend to pass into the mill outlet from the retarded boundary layer, are embraced by the strong atent i) rotational flow of the eddy produced in the sitting zone, forced away from the wall and returned into the grinding zone. Socalled bafi'ie rings 9, which are let into the inner wall of the sitting zone concentric to the axis of the grinding chamber, serve the same purpose. Coarser particles of material which pass into the sifting zone and tend to pass along the wall to the outlet from the grind ing chamber, must pass round the points of these batlle rings and thus they pass from the boundary layer into a region of higher rotational speed and are carried back into the grinding zone. The same eifect also occurs at the edges of the outlet pipes 5 which project into the sifting zone.

In the middle of the grinding apparatus, between the two outlets 5, there is provided an insertion 10, which preferably rotates, which deflects the streams of propellant, laden with extremely finely ground particles, which are issuing from opposite sides, in such manner that flow losses are reduced to a minimum. The propellant supplied to the nozzles 3 and 4 is taken from annular pipes 11 and 12.

Figure 2 shows a further embodiment of grinding apparatus according to this invention in which the walls 13 of the sifting zones form with the insertion 10 a rotating member which is mechanically moved within the stationary grinding chamber housing provided with the nozzles 3 and 4. By this arrangement the relative speed between the propellant and the wall of the: sifting chamber is kept small and the influence of the wall friction thereby reduced. On the outer periphery of the rotating walls of the sifting zones, small inclined vanes 14 are provided which cause small secondary rinsing currents which prevent the settling of dust in the gaps.

What I claim is:

l. A pulverizing apparatus comprising a generally circular casing defining a grinding zone, a sifting zone and an outlet opening, said sifting zone lying between said grinding zone and said opening and being transversely widened with respect to said grinding zone, means for the introduction of a propellant gas into said grinding zone, and means for the introduction of a propellant gas into said sifting zone.

2. A pulverizing apparatus comprising a generally circular casing defining a grinding zone, a sifting zone and an outlet opening, said sifting zone lying between said grinding zone and said opening and being transversely widened with respect to said grinding zone, said sifting zone widening abruptly at its juncture with said grinding zone to form an edge on said casing at the juncture, means for the introduction of a propellant gas into said grinding zone, and means for the introduction of a propellant gas into said sifting zone.

3. A pulverizing apparatus comprising a circular casing defining an outer annular grinding zone, an inner circu lar sitting zone and an outlet opening separated from said grinding zone by said sifting zone, said sifting zone being transversely widened with respect to said grinding zone and widening abruptly at their juncture to form a circular edge on said casing at the juncture, nozzles arranged for the introduction of a propellant gas into said grinding zone, and nozzles arranged for the introduction of a propellant gas into said sifting zone.

4. A pulverizing apparatus comprising a circular casing defining an outer annular grinding zone, an inner circular sifting zone and an outlet opening separated from said grinding zone by said sifting zone, said sifting zone being transversely widened with respect to said grinding zone and widening abruptly at their juncture to form a circular edge on said casing at the juncture, nozzles arranged for the introduction of a propellant gas into said grinding zone, nozzles arranged for the introduction of a propellant gas into said sifting zone, and a battle ring on a Wall of said sifting zone, surrounding said opening and disposed intermediate the opening and said juncture.

5. A pulverizing apparatus comprising a circular casing defining a grinding zone, a sifting zone and a pair of outlet openings in opposite sides of the casing, said sifting zone lying between said grinding zone and said openings and being transversely widened with respect to said grinding zone, nozzles arranged for the introduction of a propellant gas into said grinding zone, nozzles arranged for the introduction of a propellant gas into said sifting zone,

and a member positioned between said openings for regulating the flow of propellant gas.

6. A pulverizing apparatus comprising a circular casing defining a grinding zone, a sifting zone and a pair of outlet openings in opposite sides of the casing, said sifting zone lying between said grinding zone and said openings and being transversely widened with respect to said grinding zone, nozzles arranged for the introduction of a propellant gas into said grinding zone, nozzles arranged for the introduction of a propellant gas into said sifting zone, and a rotatable member positioned between said openings for regulating the fiow of propellant gas.

7. A pulverizing apparatus comprising a circular casing including an outer housing defining an annular grinding zone and an inner rotatable housing defining a circular sifting zone and having outlet openings in opposite sides thereof, said sifting zone being transversely widened with respect to said grinding zone, said openings being spaced from said grinding zone, nozzles arranged on said outer housing for the introduction of a propellant gas into said grinding zone, nozzles arranged on said outer housing for the introduction of a propellant gas into said sifting zone, and a rotatable member positioned between said openings forregulating the flow of propellant gas.

8. In a pulverizing apparatus including an outer housing defining an annular grinding zone, an inner rotatable housing defining a circular sifting zone, nozzles arranged on said outer housing for the introduction of a propellant gas into said grinding zone, and nozzles arranged on said outer housing for the introduction of a propellant gas into said sifting zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,237,091 Stephanoti Apr. 1, 1941 

